Heat exchangers known in the art include a heat exchanger that includes a first header common pipe and a second header common pipe which are arranged upright, a plurality of flat tubes which are arranged in a column such that side surfaces of adjacent two of the tubes face each other, which are connected at one end to the first header common pipe and are connected at the other end to the second header common pipe, and each of which has therein a refrigerant passage, and a plurality of fins separating each of spaces defined by the flat tubes into a plurality of air passages through which air flows (refer to Patent Literature 1, for example).